As semiconductor technology progresses, shrinking device dimensions has become an increasingly complex task. It is known to overcome these difficulties by using vertical integration of multiple semiconductor devices (chips), allowing either larger number of devices per unit (e.g. in memory applications) or integration of chips of different functionality, thus allowing better performance of a hybrid system (e.g. sensor, processor and memory). A technique known as Through Silicon Via (TSV) has been developed for use in vertical integration of multiple semiconductor devices. TSV is a high performance technique to create 3D packages and 3D integrated circuits (as compared to its alternatives such as package-on-package), because the density of vias is substantially higher and the length of the connections is shorter. According to TSV, conducting pillars are formed within a silicon substrate, later to be used for contacting successive chips. TSV technology provides the electrical interconnect between the components in different layers, and also provides mechanical support. In TSV technology, a via is fabricated in a silicon chip with different active integrated circuit devices or other devices fabricated by a semiconductor process, and the via is filled with metal such as Cu, Au, W, solders, or a highly-doped semiconductor material such as polysilicon. Multiple components provided with such vias are then stacked and bonded together.
A critical step in the TSV process is that of via formation, in which a pattern of contacts is etched into the silicon. In order to maintain the required via quality, it is important to control both the depth and profile of the vias.
WO 2012/098550, assigned to the assignee of the present application, discloses an optical system for use in measuring in patterned structures having vias. The system is configured and operable to enable measurement of a via profile parameters. The system comprises an illumination channel for propagating illuminated light onto the structure being measured, a detection channel for collecting light returned from the illuminated structure to a detection unit, and a modulating assembly configured and operable for implementing a dark-field detection mode by carrying out at least one of the following: affecting at least one parameter of light propagating along at least one of the illumination and detection channels, and affecting propagation of light along at least the detection channel.